The Section on Functional Neuroanatomy combines molecular and neuroanatomical methods to identify dynamic aspects of nervous system function that relate to issues of mental health, infectious disease, and drug abuse. Drug and neurotransmitter receptors are mapped using in vitro ligand binding and autoradiography. In situ hybridization histochemistry is used to localize and quantify mRNA expression of neuropeptides, monoamine transporters and synthesizing enzymes, cytokines, receptors, transcription factors, and immediate-early genes in studies of adaptive changes to pharmacological, physiological, or surgical interventions. 1) Expression of the mRNA for the immediate- early gene c-fos was used to map brain sites responsive to injections of interleukin-1 or the endotoxin lipopolysaccharide. Responsive cells in the brainstem suggest a pathway by which peripheral cytokines, as mediators of immune or inflammatory challenges, affect neuroendocrine responses. Removal of the area postrema, a circumventricular organ in the medulla, blocked the responses to intravenous interleukin-1. 2) Antidepressant drugs (fluoxetine, imipramine, phenelzine, idazoxan) were administered in an animal study of short- and long-term drug treatment. Brain systems responsive to long-term therapeutic administration include the corticotropin-releasing hormone (CRH) component of the hypothalamic paraventricular nucleus (PVN), which controls the hypothalamic-pituitary- adrenal (HPA) axis, and the hypothalamic arcuate nucleus, which is the source of major projections to the PVN and of numerous key neuropeptides such as neuropeptide Y (NPY) and beta endorphin. The results suggested that the arcuate NPY and locus coeruleus norepinephrine systems act coordinately to mediate antidepressant drug effects. Anatomical markers were combined in arcuate neurons to reveal peptide mRNA levels in neurons with identified projections to the PVN. Levels were unchanged following adrenalectomy. 3) A physiological model of memory formation is long-term potentiation (LTP), which is induced in the hippocampus in vivo by high- frequency stimulation of the perforant path. Several hours after this treatment, mRNAs for neurotrophins and neurotrophin receptors (trkB and trkC) are upregulated in a temporally and spatially discrete fashion. The data suggest that growth factors underlie the physical changes associated with memory formation.